How did you accomplish that ? Did you have the means to shut off the high
voltage ? Did you disconnect wires ?
This can be a problem with amplifiers that have a single transformer
with secondaries for the HV, filament and control systems voltages. I
would feel uncomfortable running it for a few hours, with no load at all
on the HV secondary due to whatever method might be used to remove HV
from the tubes. I think I'd prefer to find a transformer just to run the
filaments for this burn in process.
Did you run them in a test fixture that had only filament power (and a fan)
Do 3-500Z require a fan to cool them when they have only filament power
applied? Are the seals in danger of being overheated in this case?
Another precaution you may want to take before installing those new
tubes is to check the bias voltage. Many 3-500Z amplifiers have bias
voltage dependent on a single Zener diode. You may want to apply a
voltage source to the bias circuit to see what the Zener voltage really
is. Why do you need new tubes anyway? Maybe a lot of hard use on the old
ones, or maybe they weren't properly biased for some time.
DE N6KB
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